The present invention relates to a process and a device for manufacturing, by extrusion, a piece having a recessed portion in its peripheral surface.
Extrusion is advantageously used in the mass production of pieces, since it offers numerous advantages, including the obtaining of pieces having an excellent finish, a saving of material since there is no loss, and the manufacture in one operation of pieces of any cross section. The latter advantage is particularly interesting in the case of pieces of very small dimensions obtained by micro-extrusion, since it is not possible to obtain a polygonal cross section by cutting-off. Small pieces made of copper can, in fact, not be milled.
Although the process of extrusion presents many advantages, it has, however, not heretofore been useful for manufacturing pieces having recessed portions in their peripheral surface, for example transverse grooves. In fact, in order to be able to eject an extruded piece, its cross section must always be able to vary in the same direction, to allow it to leave the die by pushing by an ejector. Another limitation to the application of the extrusion process is due to the fact that, in the case of small-dimensioned pieces obtained by micro-extrusion, it is not possible to proceed with conventional ejection in forward extrusion by pushing on the rod of the piece with an ejector. In fact, as the piece is of reduced dimensions, the same applies to the ejector and such as ejector would buckle under the force to be effected.